Conventionally, a worm gear is often used to configure a portion of a gear train of a reduction gear in a power transmission system, such as an automobile component.
FIG. 20 shows a worm gear 102 such as that described above. The worm gear 102 is configured by a worm 101 and a worm wheel 100 that meshes with the worm 101. A circular arc-shaped tooth section (half-worm tooth form section) 104 is formed on the outer peripheral side of the worm wheel 100, shaped such that one end side of a helical tooth section 103 is cut into a semi-circular arc shape. In addition, a ring-shaped thick section 105 that does not form teeth is formed on the outer peripheral side of the worm wheel 100. As a result, the strength of the circular arc-shaped tooth section 104 is increased to be capable of bearing load transmitted from the worm 101. The worm 100 is designed to smoothly mesh with the worm 101 (refer to Patent Literature 1).
Patent Literature 1: Japanese Patent Laid-open Publication No. Heisei 9-250604